The invention relates to a shaft prosthesis, particularly a hip joint prosthesis having a tubular, curved hollow shaft which is tapered diametrically and in thickness and whose flexural rigidity decreases from its proximal end to its distal end at a relatively greater rate than its longitudinal rigidity. For a cement-free implantation, such an endoprosthesis is hammered into the correspondingly prepared (for example, pre-filed) bone cavity for a press-fit connection with the bone.
German Offenlegungsschrift 29 33 237 discloses a prosthesis shaft whose local elasticity and rigidity is adapted to the surrounding bone regions. This adaptation, however, relates only to cross-sectional dimensions and their coordination with forces acting in the direction of the longitudinal axis. Cross section and wall thickness decrease continuously from the upper to the lower end of the prosthesis shaft. It is a disadvantage of this construction that the deformations occurring as a result of forces attacking outside of the longitudinal axis do not conform in their behavior to the corresponding deformations of the adjacent bone region. Thus micromovements and local loosening of the prosthesis may occur.
German Offenlegungsschrift 38 44 157 discloses an endoprosthesis which is provided with a curved shaft that can be implanted into the bone cavity and is tapered in diameter and material thickness in such a way that the flexural rigidity of the shaft decreases to a relatively greater degree than its longitudinal rigidity from its end near the joint (proximal end) to its end remote from the joint (distal end). This is accomplished in this construction by reducing the flexural rigidity by providing a cut-out region extending to the end remote from the joint and disposed along the interior of the curvature of the prosthesis shaft.
It is a disadvantage of the above-noted solution that the interior of the shaft is accessible from the bottom and is thus exposed to undesirable effects during its implanted life.